In a bypass turbojet, the rotor of the fan carries a plurality of blades. Each blade includes a splined blade root that is engaged in a groove formed in the periphery of a disk, which groove is referred to as a “slot”. The slots are defined between radial projections referred to as “disk teeth” that are provided with lateral projections overlying the edges of the slots, and consequently said slots are shaped so as to retain the blade roots. The slots are open both upstream and downstream. In this specification, the terms “upstream” and “downstream” are used to designate respectively a position towards the front towards or the rear of the rotor, i.e. relative to the air flow direction.
On assembly, each blade root is engaged in its slot by sliding it in from the upstream end of the slot. The upstream ends are then closed, in particular by an annular part referred to as a “cowl rear ring”. This part is secured to the rotor disk. It also serves to hold in place longitudinal spacers inserted in the slots under the blade roots.
In the event of a blade being lost, the adjacent blade tilts because pivoting is made possible by the shape of the spacer, and it moves forwards. The blade retention system must be capable of withstanding this axial thrust.
Document EP 1 223 309 describes such a blade retention system in which the spacer head, driven by the blade, moves upstream and comes into contact with said cowl rear ring. It therefore needs to be dimensioned so as to be capable of withstanding a large force. The spacer, which also has a force transmission function, needs to be a metal element of sufficient strength to perform this role. Consequently, said cowl rear ring and the spacers inserted in the various slots are metal parts that are relatively heavy.